I did not have a single inkling of what the project was in detail or understood anything that was being talked about or written. But I was expected to 'contribute' in a performative way to show that I was useful to the team. It was perhaps the worst intro to a company you can have.
To this day I despise mob programming.
The intention is supposed to be "No pressure, come see how we work and meet the team. Feel free to join in if you see something."
There's no faster way to ramp somebody up than onboarding with a mobbing session. Typically you even use the new person's machine so the team can help make sure everything is setup for them to be productive and help work through any unexpected quirks rather than making you figure it out yourself.
If you were asked to jump in and lead with no knowledge, then yes that was terrible.
If you're open to seeing how beneficial the process can be, I'd recommend reading Software Teaming. Great book and establishes all the core rules about what makes a mob work. The most critical rule? Participation has to be voluntary.
I disagree that onboarding this way was the fastest, how could any reasonable person be expected to learn a project going in blind in an atmosphere like that?
When you aren’t in front of the keyboard, everything will continue with somebody else while the rest of the team continues to talk through the problem. On day 1, your only contribution is probably going to be familiarizing yourself with how things are setup and maybe asking some questions.
I think whoever set this up for you did a really poor job of explaining the intention.